Inkjet printers produce text and images on paper and other print media through drop-on-demand ejection of fluid ink drops using inkjet nozzles. However, when the nozzles become clogged they can stop operating correctly and cause visible print defects in the printed output. Such print defects are commonly referred to as missing nozzle print defects.
In printers that employ multi-pass print modes (e.g., scanning a print cartridge back and forth across the media), missing nozzle defects can be addressed by passing an inkjet printhead over the same section of a media page multiple times. This provides an opportunity for several nozzles to jet ink onto the same portion of a page to minimize the effect of one or more missing nozzles. Another way to address missing nozzle defects is through speculative nozzle servicing. Here, the printer causes a printhead to eject ink into a service station to exercise nozzles and ensure their future functionality, regardless of whether the nozzles would have produced a print defect.
In printers that employ single-pass print modes (e.g., media passing one time under a page-wide printhead array), missing nozzle defects have been addressed using redundant printhead nozzles that can mark the same area of a media page as a defective nozzle, or by servicing the defective nozzle to restore it to full functionality. However, the success of these solutions, particularly in the single-pass print modes, relies on a timely identification of the missing or defective nozzles.